Rough jointvetch [Aeschynomene rudis Benth.][Bayer code: none][CDFA list: B, pending change to A] Photographs Map of Distribution
SYNONYMS:Aeschynomene natans Hassler
GENERAL DESCRIPTION:Tropical emergent aquatic or terrestrial perennial, to 2 m tall. Plants are typically annual in California. Infestations are currently restricted to rice fields. Heavy infestations can reduce rice harvest yields, and seed is difficult to remove from rice grains during the milling process. Introduced from South America. Rough jointvetch has often been misidentified as Indian jointvetch [A. indica L.] or northern jointvetch [A. virginica (L.) B.S.P.] in the Southeastern U.S.
SEEDLINGS:No information available.
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MATURE PLANT:Stems often woody at the base. Stem tips densely covered with stiff hairs on dark, wart-like bases. Leaves even-pinnate compound, 4-15 cm long. Leaflets 30-60 mostly glabrous, usually 0.9-1 cm long, narrowly oblong, dotted with minute glands, typically with minutely toothed margins. Stipules narrowly triangular,+/- shield-like, with bases extending beyond points of attachment, 0.7-1.5 cm long, 0.2-0.3 cm wide, usually with minutely toothed margins, deciduous.
ROOTS and UNDERGROUND STRUCTURES:Taprooted, with many long, fine lateral roots. Associates with nitrogen-fixing bacteria.
FLOWERS:July-October. Racemes axillary, with 1-4 pea-like flowers. Corolla +/- white, purple-tinged, 8-15 mm long. Self-fertile.
FRUITS and SEEDS:Pods linear, segmented, constricted between segments along lower margins, 3-5 cm long, 0.4-0.7 cm wide, break apart into 7 to 12 square, 1-seeded segments at maturity. Stalk ~ 0.3-1 cm long. Seed +/- kidney-shaped, ~ 3 mm long, 2 mm wide.
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POSTSENESCENCE CHARACTERISTICS:No information available.
HABITAT:Edges of rice fields and nearby ditches.
DISTRIBUTION:Nearly eradicated. Sacramento Valley (ne Colusa Co.). To 20 m (66 ft). Southeastern U.S.
PROPAGATION/PHENOLOGY:Reproduces by seed. Like many legumes, seed is probably long-lived in the field, but documentation is lacking.
MANAGEMENT FAVORING/DISCOURAGING SURVIVAL:No information available.
SIMILAR SPECIES:Hemp sesbania [Sesbania exaltata
] is distinguished by having narrowly triangular stipules, to ~ 1 cm long, attached
at the base; glabrous stem tips; and linear segmented pods 15-20 cm long,
~ 0.5 cm wide, 4-sided, with +/- straight margins.
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Prevention and control: Rough jointvetch is a legume native to South America. It is currently found throughout the southeastern United States with two other Aeschynomene species, A. indica (Indian jointvetch) and A. virginica (northern jointvetch); however neither of these is present in California. The only known rough jointvetch infestation in California is in Colusa County and has nearly been eradicated. Despite its current status in California, any newfound infestations should be controlled immediately. This weed has the potential to become a serious problem in and around rice fields in California for several reasons. Infestations may interfere with harvesting, reduce yields, and decrease profits due to extensive seed cleaning costs (jointvetch seed is very difficult to separate from rice during the milling process). Additionally, most herbarium specimens collected in the southern United States were found in wet areas around rice fields or in standing water of marshes. Rough jointvetch may also be able to invade sensitive riparian areas, where control is more difficult. Cultivation of seedlings is an effective control method. It is unknown if mature plants can resprout from rootstocks. However, seeds can be transported on cultivation equipment and may survive in the soil seedbank for several years. Chemical control may be limited in rice, due to a lack of effective herbicides. The herbicide 2,4-D is ineffective on the related species, A. americana, and may also be ineffective on A. rudis. Triclopyr was recently registered in rice and may be the most effective treatment. Triclopyr should be applied at 0.25-0.38 lb ae/A. Post-flood applications should be made when jointvetch is above the water, but before flowering. Control may be reduced if plants are greater than 24 inches tall. Bensulfuron is labeled for suppression of A. virginica (post flood) in the Southern United States. However, there is no information on its effectiveness against A. rudis.